You'll lose app store app data like game saves. I always use AppBackup from Cydia. It allows you to save all the app store applications' data very easily. It backs up everything on to your phone, then you just copy the files off your phone to your pc. Then youll always have a backup that you can copy back to your phone. I know of a very easy step by step tutorial. If you want the link PM me and I'll send it to you. What's great is after you jailbreak iOS 5.1.1 and install AppBackup, you can copy all the backups over to your newly jailbroken phone. Then as you install each app one by one from the app store, you just open up AppBackup, find the app you want to restore, and tap the restore button! It's easily the best backup tool. I transfer all my app data after each jailbreak. Plus if I don't feel like installing a huge game like Infinity Blade (1GB), I just keep a copy of the backup on my pc and on my phone. If and when I ever get around to installing the app, I just go into AppBackup and restore my game to where I left off! This works for every single app store app, not just games.

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